Executive Summary
Background
Headlines in Europe recently stated: “tea tree oil – unsafe and unstable”. This undesirable media coverage overseas came as a challenge to the Australian tea tree oil industry at a time when attempts to combat low prices by better market promotion of the oil were gaining momentum. The headlines followed the release of a European SCCP (Scientific Committee on Consumer Products) opinion that concluded that insufficient data were available on the safety and stability of the oil.

Consumers and the media need to know the facts about the safety and stability of tea tree oil that, along with proven efficacy, have made the oil such a popular health care product over the last 70 years. The industry and RIRDC are addressing this situation by commissioning approved tests in order to obtain a more complete safety dossier on tea tree oil.

Aims
For this to be achieved, the oils tested must be well defined chemically for the dossier to be valid.

Methods
This investigation outlines how, from eleven commercial samples screened, three oils (one fresh, one oxidised and one, blended from commercial oils, mildly oxidised) were chosen by p-cymene content and peroxide index determination. These samples were then thoroughly defined by GC, GCMS and physical constants to determine status with respect to the ISO standard for tea tree oil before being recommended for dermal penetration and other safety parameter investigations for the dossier. The methods used were internationally accepted procedures for determining p-cymene content and peroxide value (British or European Pharmacopoeia methods), GC profiles and physical constants (ISO Standard) and GCMS (generally accepted literature procedures).

From 11 tea tree oils screened, three samples with sufficient bulk were selected for safety parameter testing.

These were found to display mean p-cymene composition percentages of 2.5, 10.5 and 19.4 which corresponded with mean peroxide values of 1.1, 11.7 and 30.5 milliequivalents of active oxygen per kg. The first of these was the only sample within the limits of the Australian and International Standards for tea tree oil. The oxidised oil failed to satisfy these standards at the following points: in the chromatographic profile, pcymene levels were high and ?- and ?-terpinene levels low even though other constituents were within the ISO Standard limits. The partially oxidised oil failed to meet the standard at p-cymene content and relative density.

Results Laboratories were surveyed for tea tree oil and product analyses where both Peroxide Value and p-cymene proportion were determined. Peroxide Values for 139 tea tree oils were found. For 77 of these the p-cymene proportion had also been determined. Records also showed aged oils stable for from 3-10years if stored correctly.

As a result of this investigation, it is suggested that oxidised tea tree oils are always seen to be associated with high p-cymene contents and sometimes high peroxide values. Of the samples recorded, one with low peroxide value, showed high p-cymene content. This is not unexpected, as it is known that peroxides are unstable and decompose to oxidation products such as 1,2,4-trihydroxymenthane. Conversely some with high peroxide values were low in p-cymene but only when heat and/or rapid air movement removed the lower boiling terpenes including p-cymene. The oxidised oil provides an oil that would simulate an oil from a bottle which had been frequently opened for use by the consumer and inadvertently let deteriorate.

Implications With the difficulty in measuring and identifying the degradation products due to their instability and poor documentation, p-cymene concentration seems a better determinant for oxidation than any other method.

Sufficient well accepted Standards exist for this to be an easy analysis. The testing planned for the selected oils will be of economic benefit as a better defined oil will lead to more sales and be of social benefit as the safety and stability of the oil become recognised.

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